Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$39.95	10.459%	$44.1284	$44.13	$44.15	$44.10
Purchase #2	$73.96	11.809%	$82.6939	$82.69	$82.70	$82.70
Purchase #3	$230.53	7.230%	$247.1973	$247.20	$247.20	$247.20
Purchase #4	$118.31	10.740%	$131.0165	$131.02	$131.00	$131.00
Purchase #5	$206.65	7.152%	$221.4296	$221.43	$221.45	$221.40
Purchase #6	$100.45	4.860%	$105.3319	$105.33	$105.35	$105.30
Purchase #7	$210.88	13.872%	$240.1333	$240.13	$240.15	$240.10
7 purchase totals =	$980.73		$1,071.9309	$1,071.93	$1,072.00	$1,071.80